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The synthesis and structures of two types of molecules and the complete series of oxo/sulfido/silyloxo molybdenum complexes are described. The sulfidation reactions have described the utility of [Ph.sub.3]SiSH and [Pr.sub.3.sup.i]SiSH as reagents for [Mo.sup.VI]-based oxo-for-sulfido conversions.

The x-ray diffraction studies of ternary and quaternary molybdenum cluster chalcohalides show that these are positively charged zigzag chains containing Te-halide ions.

The redox chemistry and spectroscopy of novel tungsten sulfite polyoxotungstates are presented and then compared with molybdenum sulfite analogue and related sulfate species. The results have shown that the unpaired electron in [alpha]-[[[W.sub.18][O.sub.54][(S[O.sub.3]).sub.2]].sup.5-] is delocalized over a number of atoms in the polyoxometalate structure.

A dimolybdenum molecular pair, [Mo.sub.2][(DAniF).sub.3][([mu]-OH).sub.2][Mo.sub.2][(DAniF).sub.3], is synthesized and characterized by using X-ray crystallography. The results have provided an interesting case of single-crystal-to-single-crystal (SCSC) transformations and described the deprotonation process affected by dioxygen.

A general and effective one-step procedure is presented for the synthesis of [beta]-sulfonamidodisulfides directly from N-tosyl aziridines in a regio- and stereospecific manner under neutral conditions and without using any Lewis acid or base. A number of [beta]-sulfonamidosulfides are synthesized in tandem, multistep reactions.

A series of new complexes are synthesized from [[(Zn[O.sub.6])[[([As.sub.3][O.sub.3]).sub.2][Mo.sub.6][O.sub.16]].sup.4-] and [[[H.sub.x][As.sub.2][Mo.sub.6][O.sub.26]].sup.(6-x)-] clusters as SBUs under hydrothermal synthesis conditions and their structures are determined by single-crystal X-ray diffraction analysis. The analysis has shown that it is possible to use molybdenum arsenates as SBUs building up functionalized open-framework solid-state materials.

Mono and diprotonated species of [[I[Mo.sub.6][O.sub.24]].sup.5-] were synthesized and structurally characterized. These protonated species react with methanol in a selective manner to give methylated Anderson-type anions while the unprotonated [[I[Mo.sub.6][O.sub.24]].sup.5-] anion does not react with methanol under similar conditions.

New ternary early transition metal pnictides, [Ti.sub.0.79(1)][Mo.sub.1.21][Sb.sub.4] and [Ti.sub.0.86(2)][Mo.sub.1.14][As.sub.4] were synthesized and their crystal structure, electronic structure and physical properties were studied. Both the compounds were found to crystallize in the Os[Ge.sub.2] type, space group C2/m and no long-range order, resulting in subgroups, was found to occur between the Ti and Mo atoms.

The formation of supramolecular networks of [[(Cp*Mo).sub.2][As.sub.2][S.sub.3]] (Cp*=[C.sub.5][Me.sub.5]) from a mixed As/S-ligand complex and copper halides are described. The assembly of the building blocks is promoted by the lone pairs of the central monosulfide bridge of the organometallic complex in all the products and the nature of the products depends on the copper halide used.

A major obstacle to understanding the reduction of [N.sub.2] to N[H.sub.3] by nitrogenase has been the impossibility of synchronizing electron delivery to the MoFe protein for generation of specific enzymatic intermediates. When an intermediate is trapped without synchronous electron delivery, the number of electrons, n, it has accumulated is unknown. Consequently, the intermediate is untethered from kinetic schemes for reduction, which are indexed by n. We show that a trapped intermediate itself provides a 'synchronously prepared' initial state, and its relaxation to the resting state at 253 K, conditions that prevent electron delivery to MoFe protein, can be analyzed to reveal n and the nature of the relaxation reactions. The approach is applied to the '[H.sup.+]/[H.sup.-] intermediate' (A) that appears during turnover both in the presence and absence of [N.sub.2] substrate. A exhibits an S = 1/2 EPR signal from the active-site iron-molybdenum cofactor (FeMo-co) to which are bound at least two hydrides/protons. A undergoes two-step relaxation to the resting state (C): A [right arrow] B [right arrow] C, where B has an S = 3/2 FeMo-co. Both steps show large solvent kinetic isotope effects: KIE [approximately equal to] 3-4 (85% [D.sub.2]O). In the context of the Lowe-Thorneley kinetic scheme for [N.sub.2] reduction, these results provide powerful evidence that [H.sub.2] is formed in both relaxation steps, that A is the catalytically central state that is activated for [N.sub.2] binding by the accumulation of n = 4 electrons, and that B has accumulated n = 2 electrons. intermediate | kinetic isotope effect

A detailed mutational analysis of the MoeA protein from Escherichia coli, which mediates ligation of Mo to molybdopterin, is described. Crystal structures of the functionally characterized MoeA variants revealed no major structural changes, indicating that the functional differences observed are not due to disruption of the protein structure.

The halide-bridged tetranuclear clusters, [cis-Mo2(DAniF)2]2([mu]-X)4, X=Cl, Br, and I are produced by reactions of [cis-Mo2(DAniF)2(NCCH3)4](BF4)2, DAniF= N,N'-di-p-anisylformamidinate, with an excess of anhydrous. All three compounds show two reversible one-electron oxidation processes with potential separations between the two oxidation processes of 540, 499, and 440 mV.

A study synthesized and crystallographically characterized a pair of isomeric cyclic triads containing three quadruply bonded [Mo2] units, [[Mo2(cis-DAniF)2].sup.2+] bridged by six fluoride. For the [alpha] isomer, the three [Mo2] units are oriented in two orthogonal directions.

The dodecamolybdocerate (IV) anion, (NH4)6H2(CeMo12O42).9H2O) is synthesized and its Ce(111) form is obtained by exhaustive electrochemical reduction. Both forms are fairly stable in pH 0.0 media but the stability decreases when the pH increases.

The novel molybdenum oxo-imido bis-(aryloxide) complexes are prepared by the salt elimination reactions of [Mo(N'Bu)(O)[CI.sub.2](DME)] with the lithium aryloxide of from the cycloaddition reactions of tert-butyl isocyanate with the appropriate molybdenum dioxo bis(aryloxide) complex. The geometry around the metal in complexes is described as a distorted trigonal bipyramid, with the imido and pyridine ligands occupying axial positions and the oxo and aryloxide ligands in the equatorial plane.

Explorations of the reactivity of Fe/Mo/S clusters of some relevance to the FeMoco nitrogenase has led to new double-fused cubane clusters with the Mo2Fe6S8 core as derivatives of the known (Cl4-cat)2Mo2Fe6S8(PPr3)6 (l) fused double cubane. New clusters are obtained by substitution reactions of the PPr3 ligands with Cl(super -), BH4(super -) and N3(super -).

The existence of a three-member electron-transfer series of single cubanes [(Tp)MoFe3S4](super z) (z = 3-, 2-, 1-) and a four-member series of double cubanes [(Tp)(sub 2)Mo2Fe6S8L4](super z) (z = 4-, 3-, 2-, 1-) with L = F(super -), Cl(super -), N3, PhS(super -) is showed by electrochemical methods, cluster synthesis and X-ray structure determinations. The synthesis and structure of [(Tp)(sub 2)Mo2Fe6S8F2.H2O](super 3-), a new topological analogue of the P(super N) cluster of nitrogenase, is presented (Tp = hydrotris(pyrazolyl)borate(1-)).

Hexasubstitution of apical triflate ligands in the octahedral clusters [M](sub 2) [Mo(sub 6X(sub 8)(CF(sub 3)SO(sub 3)(sub 6)] (M=n-Bu(sub 4)N or Cs, X=Br or I) and monosubstitution in [n-Bu(sub 4)N](sub 2)Mo(sub 6)Br(sub 13)(CF(sub 3)SO (sub 3)] was carried out in tetrahydrofuran with simple pyridines and then extended to organometallic pyridines. The organometallic pyridines yielded cluster-cored stars, and dendronic polyallyl and polyferrocenylpyridiens yielded cluster-coated polyallyl and polyferrocenyl dendrimers and dendrons.

A series of complexes with the general formula (n-Bu4N)2[M2O2(mu-Q)2(dmit)2] (where M = Mo, W;Q = S, Se;dmit = 1,3-dithioie-2-thione-4,5-dithiolate) are prepared. Fragmentation of the trinuclear cluster (n-Bu4N)2-[Mo3(mu3-S)(mu-S2)3(dimit)3] in the presence of triphenylphosphine gives the dinuclear compound (n-Bu4N)2[M2O2(mu-S)2(dimit)2} {n-Bu4N)2[2]}.

The mechanistic issues associated with the production of terminal phosphide complexes of molybdenum by reaction of white phosphorus (P4) with reactive trivalent molybdenum trisamides are studied. Post-rate determining steps of the P4 activation process were examined in a search for minima on the reaction's potential energy surface, leading to the proposal of two plausible, parallel, bimetallic reaction channels.

The syntheses, structures and magnetic properties of unprecedented two-dimensional (2D) layered Cu(II)-M(V) complexes [Cu(L)](sub 3n)[M(CN)(sub 8)](sub 2n).6nH2O (M = Mo (2), W (3) and L = macrocyclic ligand) with honeycomblike structures, formed by self-assembling [Cu(L)](super 2+) (1) and [M(CN)(sub 8)](super 3-) in a ratio of 3:2 are described. The temperature- and field-dependent magnetic features show that paramagnetic Cu(II) and M(V) centers are ferromagnetically and antiferromagnetically coupled through cyanide bridges.

A description of the synthesis and characterization of sulfo-bridged dinuclear Mo-Cu complexes related to the active site of [MoCu] carbon monoxide dehydrogenase is presented. The dinuclear Mo-Cu complex, [O(sub2)MoS(sub2)Cu(SPh)](super 2-), is prepared from the reaction of [MoO(sub2)S(sub2)](super 2-) with [Cu(SPh)(sub3)](super 2-).

Evidence supports that metal-based isomerizations could play an important role in the mechanism of some molybdoenzymes. Data presented indicates that there are both oxidation state and donor atom dependencies in the relative stabilities of the cis and trans isomers of oxo-Mo centers.

An unusual reductive degradation of an otherwise robust and chemically inert molybdenum polyacid using PPh3 as a reducing agent in the presence of a N3-donor 2-[(arylamino)phenylazo]pyridine is presented. The reaction results in a monometallic molybdeum complex with complete removal of oxides and the reduced metal ion are trapped by the ligand.

Molybdenum phosphide (MoP) and supported molybdenum phosphide (MoP/gamma-Al2O3) are prepared and characterized by the temperature-programmed reduction method. Co that is observed to get adsorbed on the surface of MoP/Al2O3 shows a characteristic band at ~2037 per cm because of the linearly adsorbed CO on Mo(super delta+) sites.

The compounds ((super t)BuCO2)3M2(mu-O2CCO2)M2(O2C(super t)Bu)3(M4OXA), where M=Mo or W, are shown by analysis of powder X-ray diffraction data to have extended lattice structures wherein oxygen atoms from the oxalate and pivalate ligands of one M4OXA molecule are linked to metal atoms of neighboring molecules. The Raman, resonance Raman, and variable-temperature electronic spectra of these oxalate-linked 'dimers of dimers' reveal the richness of orbital mixing in these extended pi systems, both in the ground and excited states.

The eta(super 5)-indenyl complex [(eta(super 5)-Ind)(Cp)MoL(sub 2)](super 2+), L = phosphine, phosphite, undergo two closely spaced one-electron reductions to the corresponding monocationaic and (eta(super 3)) neutral complexes. The combination of X-ray experiments and the DFT calculations shows that the change from eta(super 5) to eta(super 3) hapticity in the Mo-indenyl interaction occurs incrementally.

The twelve compounds containing two quadruply bonded Mo2(DAniF)(sub 3) (DAniF = N,N'-di-anisylformamidinate) units linked by dicarboxylate anions are prepared in high purity and good yields and these compounds are characterized by crystallography and NMR. The dinuclear pairs display electrochemical behavior that is controlled by the nature of the bridging dicarboxylate group.

The syntheses and structural and physical characterization of the compounds [Cu(bipy)(sub 2)](sub 2)[Mo(CN)(sub 8)].5H2).CH(sub 3)OH (1) with bipy = 2,2'-bipyridine and M(super II)[Mo(super IV)(CN)(sub 8)].xH20 (2 with M Cu, x = 7.5; 3 with M = Mn, x = 9.5) are presented. The compounds displayed two different types of photomagnetic effects, where the first effect was based on chemical reaction (photooxidation) and the second effect resulted from a photoinduced electron transfer between two different metallic centers.

The preparation and crystal structures of two modifications of Hg2MoO4 are reported. At high temperature Hg2MoO4 (the beta-modification) crystallizes with a structure, where MoO4 tetrahedra are linked through Hg2 dumb-bells, thus forming infinite zig-zag chains and at low temperature Hg2MoO4 (the alpha-modification) contains MoO6 octahedra, which are linked via common edges to form zigzag chains, which are further linked via Hg2 dumb-bells, thus forming puckered two-dimensionally infinite sheets.

The syntheses and structures of two clusters containing 12 Mo-Mo quadruple bonds,[Mo24(C12H12O4)24](C5H5N)12 and Mo24(C8H4O4)24, are reported. The 12 paddlewheel building blocks and 24 ligands self-assemble into cuboctahedral and anticuboctahedral polyhedra, respectively depending on the manner in which the two halves of the cluster are aligned.

Molybdenum monooxo compounds MoO(Ar)(sub 4-n)Cl(sub n) (n=0-2, Ar=2,6-Me2C6H3 or 2,6-i-Pr2C6H3) were synthesized starting from the dioxo percursor MoO2Cl2. The complexes were characterized spectroscopically and by X-ray diffraction.

X-ray diffraction, Mossbauer spectroscopy, positron lifetime measurements, high resolution transmission electron microscopy observations and magnetization measurements were used for examining the relationship between the phase evolution, nanostructure, exchange coupling and magnetic properties of Nd8.4Fe86Mo1.1B4.5 magnets prepared by melt spinning (MS) and mechanical milling (MM).

Magnetic structure and dielectric response of [Ca.sub.3]CoMo[O.sub.6] are analyzed as a function of temperature and applied magnetic field. Dielectric measurements have disclosed the presence of magnetoelectric coupling below magnetic ordering temperature and have described the existence of a correlation between magnetic structure and dielectric properties.

A sequential, one-pot, multistep reaction in presence of potassium selenocyanate and benzyltriethylammonium tetrathiomolybdate ([[BnN[Et.sub.3]].sub.2]Mo[S.sub.4]) was performed to prepare a variety of N-alkyl-[beta]-aminodiselenides in high yield from sulfamidates under mild reaction conditions. The approach could efficiently be applied for the synthesis of selenocystine, 3,3'-dialkylselenocystine, and 3,3'-diphenylisoselenocystine and their direct incorporation into peptides.

X-ray diffraction analysis has shown the presence of the targeted molecular compound, which has the {[Mo.sub.18][O.sub.18][S.sub.18][(OH).sub.18]} host templated by the [[[Mo.sub.3][S.sub.4][(Hnta).sub.3]].sup.sup 2-] guest, and the structure has shown an additional molecular moiety corresponding to a dinuclear unit {[Mo.sub.2][O.sub.2][S.sub.2]}. The dinuclear individual species in solution has given rise to cis-trans equilibrium, while in the presence of the oxothiomolybdenum ring the dinuclear unit is maintained as a frozen cis complex.

The article presents a new two-step procedure that can be used for the preparation of the various hybrid organic/inorganic complexes based on the different electroactive tetrathiafulvalene-functionalized diphosphanes. The molecular structures and the properties of these compounds are also discussed.

Numerous analyses are conducted to explain the crystal structure, synthesis and properties of praseodymium molybdate, [Pr.sub.2][(Mo[O.sub.4]).sub.3] compound. The various a antiferromagnetic interactions of the compound are also discussed.

The density functional theory (DFT) study is conducted to explain the electron paramagnetic resonance (EPR) parameters of the model compounds of dimethyl sulfoxide reductase. The magnetic circular dichroism spectrum observed in these compounds is also discussed.

The article explains the preparation, as well as the properties of the vanadium(II) heptacyanomolybdate(III)-based magnet, which is shown to exhibit an extremely high Curie temperature.